Filling out a date range with values based on most recent

I have a table like this:
tblChanges
Date     Value
1/1           3
5/1           5
7/1           8

And another like this:
tblDates
Date
1/1
2/1
3/1
4/1
5/1
6/1
7/1
8/1

I want to combine these tables into this
Date  Value
1/1    3
2/1    3
3/1    3
4/1    3
5/1    5
6/1    5
7/1    8
8/1    8

So in other words, it's like a left join from tblDates on tblValues where nulls yield that last (i.e. most recent) change value.  Restated, I want to know what change value is in effect for each date in the list.  If nothing matches, take the most recent.

This could be done with Domain functions (like DLast), but that's very cumbersome.  Is there a better way?
shachoAsked:
Who is Participating?

[Webinar] Streamline your web hosting managementRegister Today

x
 
Phillip BurtonConnect With a Mentor Director, Practice Manager and Computing ConsultantCommented:
Here's the SQL for the query with non-equal comparisons. It might not be as slow as I was fearing:

SELECT qryRelevantDate.Date, tblChanges.Value
FROM (SELECT tblDates.Date, Max(tblChanges.Date) AS MapDate
FROM tblDates INNER JOIN tblChanges ON tblDates.Date >= tblChanges.Date
GROUP BY tblDates.Date) as qryRelevantDate INNER JOIN tblChanges ON qryRelevantDate.MapDate = tblChanges.Date;

Open in new window

0
 
Phillip BurtonDirector, Practice Manager and Computing ConsultantCommented:
It may be cumbersome, but it's probably the best way.

If this was SQL Server, then you could use the LAG function, but that's not present in Access.

Outside of DLast, you would have to do some JOINs with non-equal comparisons, and if you have a big table, that would get slow - so Domain functions are probably the best for Access.
0
 
Phillip BurtonDirector, Practice Manager and Computing ConsultantCommented:
This is the output:

Date	Value
01/01/2014	3
02/01/2014	3
03/01/2014	3
04/01/2014	3
05/01/2014	5
06/01/2014	5
07/01/2014	8
08/01/2014	8

Open in new window

0
 
Gustav BrockCIOCommented:
Why not pick the values directly:

Select
    tblDates.Date,
    (Select Max(tblChanges.Value)
    From tblChanges
    Where tblChanges.Date <= tblDates.Date) As [Value]
From
    tblDates

/gustav
0
 
shachoAuthor Commented:
Yep, that does the trick, Phillip.
Thanks all for your comments!

Cheers,
0
All Courses

From novice to tech pro — start learning today.